1. Field of the Invention
The present invention relates to an ultrasonic transducer for use in a fluid medium.
2. Description of Related Art
Ultrasonic transducers are known in various fields of use from the related art. For example, ultrasonic transducers are used in automotive engineering in ultrasonic flow meters, for example, in the exhaust system and/or in the intake system of internal combustion engines. Examples of such ultrasonic transducers are described in published German patent application document DE 10 2007 037 088 A1 or German Patent Application DE 10 2008 055 126.0 of the applicant (which is not believed to be prior art). Ultrasonic flow meters are based in many cases on two ultrasonic transducers, which are situated offset in a flow tube in the flow direction and mutually send one another ultrasonic signals. Measuring systems may also be used in which at least one reflector is provided, for example, in the form of plug-in sensors. Further applications of ultrasonic transducers are, for example, filling-level meters or distance meters, for example, in so-called Park Pilot systems.
In many cases, ultrasonic transducers have an electroacoustic transducer element in the form of a piezoceramic. In order to achieve an impedance adjustment, i.e., in particular a reduction of reflection losses at the interface between the ultrasonic transducer and the fluid medium in which the ultrasonic transducer is to be used, in many cases so-called adjusting bodies are used, which ensure at least partial impedance compensation between the piezoceramic and the impedance of the fluid medium. For example, ultrasonic transducers based on a piezoceramic in conjunction with so-called λ/4 impedance adjustment layers are known. Examples of such adjusting bodies, which may also be used in the scope of the present invention, are described in published German patent application document DE 10 2007 037 088 A1 or German patent application DE 10 2008 055 126.0.
Furthermore, ultrasonic transducers having a housing in the form of a one-piece sleeve and a ring-shaped rear cover are known from the related art. Such ultrasonic transducers are used, for example, in Park Pilot systems. In this case, the piezoceramic is typically first electrically contacted in that, for example, wires are welded to the piezoceramic and to the contact pin connected to the cover ring. Subsequently, the piezoceramic is then typically held with the aid of a vacuum pad gripper through the cover ring and inserted into the sleeve jointly with the cover ring and the connecting wires. During this procedure, the connecting wires receive the bending shape which is desired inside the later ultrasonic transducer for the purpose of ideal durability. Before the vacuum pad gripper may be removed, an adhesive must typically be activated between the piezo and the sleeve, which occurs in many cases in the form of ultraviolet radiation, which is typically also introduced through the cover ring.
In practice, this type of assembly is, however, associated with various technical requirements and disadvantages in practice. Thus, one-piece transducer sleeves must typically be implemented as very deep, because an interior of the transducer sleeves must be filled up with a specific quantity of damping material. Furthermore, this depth of the transducer sleeve is typically required to allow fastening of contact pins or re-contacting in order to ensure an appropriate guide length for a precisely aligned installation, for example, in a plug-in sensor housing, or to make the general handling of the entire transducer easier. However, the handling during the construction process is typically made more difficult by this depth of the transducer sleeve, because the piezoelement must be sunk deep into the transducer sleeve. Electrical contacting of the piezoceramic which is suitable for mass production is then only possible with difficulty inside the sleeve. In contrast, if the electrical contacting of the piezoceramic is performed before the joining with the optional adjusting body, the piezoceramic, the connecting wires, the contact pins, and optionally the transducer cover or transducer cover ring must remain fixed or positioned relative to one another in the scope of the joining procedure. Such a method is extraordinarily complex.